WO1999032066A2 - Bone cement for natural teeth and dental implants - Google Patents

Abstract

The use in the dentistry and maxillo-facial fields, more particularly in parodontology and implantology, is proposed of an osteocompatible cement mixture for operations such as bone reconstructions or as filling material of cavities that formed naturally or as a consequence of operations carried out on the maxillar bones.

Description

USE OF BONE CEMENT FOR THE FIXING AND STABILIZATION OF NATURAL TEETH AND/OR DENTAL IMPLANTS.

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TECHNICAL FIELD

The present invention relates to a new use in the field of parodontology and of dental implantology of a bone cement of known composition and specifically and uniquely used in orthopaedic surgery until now.

More particularly, the new use according to the present invention concerns the rebuilding and/or substitution of a part of maxillo-facial tissue with which it results therefore to be possible to stabilize a natural tooth and/or a titanium implant with its relative dental prothesis.

DESCRIPTION OF THE INVENTION In parodontology, the operational difficulties found in patients affected by mobility of one or more teeth are known. Such a mobility is due to the destruction of the bone and of the parodontal bond and may be caused by several factors among which for example, occlusion problem, excessive loads, scarce hygiene that determines the occurrence of inflammations and infections. In order to defeat these pathologies, the state of the art comprises in most cases resorting to surgical operations which aim at the elimination of granulation tissues and at the implant of some bone that originates from the patient himself or at the use of suitable materials, such as hydroxylapathite .

The use of different types of implants, all normally made of titanium, in the field of implantology is known in the art . Once suitably fixed to the bone structures, said implants are provided with suitable means for the support of one or more dental protheses, according to the specific case dealt with. According to an operational methodology which is well known in the art, whenever the bone reaches a thickness that is sufficient to guarantee a correct positioning of an implant, generally for the dental surgeon the need arises to carry out a boring within the bone, for example inside the mandibular bone, by suitable equipment such as cutters or other tools.

Said boring is made to have such a size that it allows a precise and calibrated insertion of the implant which is generally made of titanium, which is also threaded inside according to a suitable pitch so as to subsequently receive the actual dental prothesis .

Said prothesis is in fact provided with a screw whose threading has a pitch which is the same as that of the above mentioned implant which is suitable for receiving the above mentioned prothesis which has been duly screwed.

The main drawback of an operation of this type is given by the long waiting times which are necessary for the titanium implant to acquire solidity and firmness inside the bone, said times being in the range of months, generally between six and nine, or even more.

It results in fact to be necessary that the implant, which plays the role of being a support for the future capsule, becomes an integrating part of the bone which it was introduced into, for example of the mandibular bone, said osseointegration process being made possible by treating the outside surface of the titanium used, with a hydroxylapathite .

In fact hydroxylapathite is a biological material in itself as it is the mineral part of a bone, even if bone hydroxylapathite is structurally different as it has a laminar structure surrounded by bone cells, by collagen fibrils and submerged in protein mucus fluid, whereas implantary hydroxylapathite is a synthesis material, which has been sintered and compressed so as to increase its resistance.

Unfortunately, as it was already mentioned above, in order for such a condition to be fulfilled, many months are necessary from the moment when the implant has been inserted, and only at a second stage, a long time after the beginning of the operation, it is possible to complete the job by positioning the prosthetic tooth.

However, such a type of operation does not result to be possible when in a given patient the bone available results to be so insufficient in terms of quantity not to possess that minimum safety depth which is capable of guaranteeing a correct fitting of the implant inside the bone itself.

Therefore, in such a clinical situation, there is found to be missing the necessary thickness in order to let the dental surgeon carry out a boring having an optimal depth and which is suitable for receiving the implant of which above .

It is necessary to stress in fact that a boring which is little deep would not be capable of supporting the overlying implant in a durable and correct way, as much as on the other hand, it results to be impossible to get down beyond a certain threshold because in the area underneath the bone, nerves or other anathomic structures may be located, among these the maxillar sinus, which must not be naturally dented.

Therefore in such circumstances the dental surgeon finds himself faced with the difficulty of rebuilding the tooth so as to be able to create that thickness that is necessary to him for the correct positioning of the implant as it was described above.

This rebuilding is carried out by filling the- volume of the bone which is involved in the implant, with a suitable material which generally consists of human bone (autologous transplant) , for example excised from the chin or from the hip, or with hydroxylapathite or else with bovine or demineralised human bone. Inside said material the implant is therefore inserted and the superficial part of the whole volume can then be covered with resorbable membranes or not, such as for example a Goretex® film, said membranes having the specific task of isolating the above mentioned filling material from the surrounding mucose.

Once said membrane has been positioned, it is necessary to wait for a period of time that varies between six and nine months, so as to allow the time for the material to solidify before applying the final capsule duly screwed within the implant in a similar way to that previously described.

A considerable drawback of such a type of operation is that once again, a very long waiting time for the patient is necessary before finding his new tooth available. A further disadvantage is furthermore relative to the fact that said operation is not always successful as there is a very high risk that the implant does not have enough stability because of its unsatisfactory tightness of the material employed for the rebuilding and/or substitution of the bone, once the new capsule has been screwed in.

It is not always that, in case such a situation occurs, the operation can be repeated, this involving a remarkable waste of money, energies and time with a considerable damage caused to the patient that finds himself still compelled to wait for a long time before having his problems solved.

It is furthermore known in the art, as it is for example found in Italian Patent N° 1234978, the -employment in dentistry of bicomponent cement mixtures formed with a monomer liquid phase and a polymer solid phase, combined in suitable percentages so as to obtain a rapidly solidifying resin material.

According to a preferred formulation of said cement mixture, 97% by weight of the polymer phase consists of poly ethylmethacrylate, whereas the remaining 3% by weight consists of a catalyst, such as benzoyl peroxide; instead, 99.1% of the monomer phase consists of monomethyl methacrylate, whereas 0.89% consists of an accelerator, such as N-N-dimethyl-p-toluidine, and the remaining percentage by weight consists of a stabilizer such as hydroquinone .

Such mixtures can furthermore comprise the employment of fluoride salts that are additioned to the solid phase on account of the fact that fluorine brings about an advantageous increase in size of the hydroxylapathite crystals present in the bone tissue as a mineral component, fact that causes a remarkable improvement of the mechanical properties of the bone straucture.

Furthermore, the presence of fluoride ions favours osteoblast stimulation, these being the cells that are directly responsible for the formation of the bone tissue.

The cement mixtures dealt with above exhibit several advantageous properties related to their biocompatibility with the bone tissue with which they have to matched, not causing disadvantageous reject-related phenomena, and eliminating at source those implant detachment problems that arise in case acrylic resin based cements are used as it happens for example in the orthopaedic field. The Applicant is aware of the fact that mixtures of the above described type are used in orthopaedics, particularly for the application of a prosthetic hip.

It is an object of the present invention that of employing these advantageous cement mixtures (heretofore denominated as "bone cement" for the purpose of the present specification) in the fields of parodontology and dental implantology, said mixtures having been so far exclusively devised and employed for orthopaedic surgery, and, particularly, for hip protheses .

According to the present invention, in case for the dental surgeon the need arises to have to set out for an operation of the surgical parodontal type in order to stabilise and/or insert an implant into a volume of bone which has a sufficient thickness to host it, he is faced with having to dig an undercut cavity which is suitable for receiving the bone cement and is capable of making it possible for the bone to remain integral with the bone itself . According to the present invention, after its completion, the cavity is filled up with the bone cement of which above, in case an implant or a totally extracted tooth is being dealt with, and these are inserted into the cement before its polymerisation phase has gone to completion. The operational modality according to which the base surface of the cavity is made larger, thus creating a suitable anchoring recess, gathers a remarkable importance as once hardened, the bone cement is made to acquire such a shape that it guarantees the certainty that the cement itself and the tooth or implant that has been prepared along with it, result to have been stabilised.

Furthermore, as it was reminded above, on account of the composition itself of the bone cement employed, it is able to establish an intimate bond with the bone tissue, which it is in contact with, therefore making the prothesic implant perfectly integral with the bone structure within which it is positioned. A further advantage given by the use of said cement composition in the fields of parodontology and of dental implantology is that of the very limited time ranges needed by this cement for setting, this making it possible to position the new tooth in the arch during the same session or very shortly after it, without forcing the patient to be subjected to uncomfortable conditions for many months.

According to a further operational modality of the present invention, it results to be possible to implant the capsule directly into the bone cement, instead of resorting to positioning the implant first, and the capsule itself on it.

This is made possible both by the very limited time frames that this operation requires, on account of the use made of the bone cement mentioned above, and by the absolute certainty that the cement together with the implant therein included does not move from its position at all, even a few minutes after it has been positioned.

On the other hand, in case the dental surgeon does not find out he has a thickness that is sufficient for fixing the implant and in case he finds himself forced to carry out a partial reconstruction of the bone, it results to be evident how the employment of the above mentioned bone cement brings about undoubted and considerable advantages.

In such a type of operation, in fact, the bone cement used as a filling and adhesion material for the implant allows a very good and rapid setting, eliminating the risk of rejection, whose occurrence would unavoidably determine the detachment of the device fixed by the dental surgeon. In an analogous manner as that outlined previously, even in this case, in order to make sure that a higher degree of solidity and of safety is reached by the implant, it is possible to prearrange a number of anchoring points for the cement, once solidification has gone to completion.

For instance, canals or holes can be dug on the side surfaces of the portion of bone that must be filled up and reconstructed with the bone cement object of the present invention, said canals or holes working as anchoring means for blocking the material once it has been positioned in its location which is suitable for hosting it.

Claims

1. Use in the dentistry and maxillo-facial fields, more particularly in parodontology and implantology, of an osseocompatible cement mixture for operations such as bone reconstructions or as filling material of cavities that formed naturally or as a consequence of operations carried out on the maxillar bones.

2. Use according to claim 1, characterised in that said osteocompatible mixture is a bicomponent mixture.

3. Use according to claim 2, characterised in that the solid phase of the bicomponent mixture is of a polymer type and that the liquid phase of the bicomponent mixture is of a monomer type.

4. Use according to claims 2 and 3, characterised in that the cement mixture comprises a polymer phase, 97% by weight of which consisting of polymethylmethacrylate and the remaining 3% by weight consisting of a catalyst, such as for instance benzoyl peroxide, whereas 99.1% of the monomer phase cosists of monomethyl methacrylate, 0.89% of it consists of an accelerator, such as for example N-N-dimethyl-p- toluidine, and the remaining percentage consisting of a stabilizer, such as for instance hydroquinone .

5. Use according to anyone of the preceding claims, characterised in that the cement mixture comprises fluorine salts which are suitable for being additioned to its solid phase.